July 3 (Bloomberg) -- Four wastewater wells used in oil and
natural gas drilling may be responsible for triggering 20
percent of all earthquakes in the central and eastern U.S. from
2008 to 2013, according to a study published today in the
journal Science.

The wells are used to dispose of high volumes of wastewater
released from underground rocks when they are fractured using
modern oil-drilling techniques. The four wells are likely
responsible for a dramatic rise in earthquakes near Oklahoma
City since 2009, according to the research.

Oklahoma has had more earthquakes than California so far
this year, making it the most seismically active state in the
continental U.S. and raising suspicions that drilling activity
is influencing a surge in temblors there. The state had 238
earthquakes with a magnitude 3.0 or greater through June, more
than double the number in California, which has historically
ranked second in earthquakes behind Alaska.

Scientists studied wastewater-injection volumes, geologic
information and data from earthquake sensors to show that fluids
pumped into the wells increased underground pressures and spread
them. The area of elevated underground pressure grew in a way
that overlapped with a “migrating front” of earthquakes
centered near Oklahoma City.

The data showed that water pumped into wastewater wells can
increase and affect underground pressures as far away as 35
kilometers (22 miles), potentially triggering earthquakes at
faults that would have previously been considered too distant.

Researchers from Cornell University, University of
Colorado, Columbia University, and the U.S. Geological Survey
collaborated on the study.